Technical Notes

Reliable spectroradiometry takes a lifetime of work and attention to master. Unreliable spectroradiometry is much easier to accomplish1 all it takes is missing a single critical point, like the interdependence of source time variation and detection system bandwidth or the source spectral bandwidth and instrument chromatic properties.

This discussion is restricted to the general use of Incoherent Light Sources, such as arc lamp or quartz tungsten halogen sources. Diffraction and coherent effects are excluded. The emphasis throughout this section will be on the collection of light.

Newport's Oriel® Instruments light source offerings are varied and significant. With so many options, it can be difficult to choose the best system for your application. For light source technical information and a summary of the major advantages of each type of light source please view this guide.

An FT-IR Spectrometer is an instrument which acquires broadband NIR to FIR spectra. Unlike a dispersive instrument, i.e. grating monochromator or spectrograph, FT-IR Spectrometers collect all wavelengths simultaneously. This feature is called the Multiplex or Felgett Advantage.

In this section we give a brief introduction to getting light into a monochromator, and how much you can expect to get out. While the emphasis is on coupling Oriel Light Sources to Oriel Monochromators, the same general principles apply to collecting light from any source for analysis. Specifically, all of the collection principles we will cover here may be applied to spectrographs as well as monochromators.

Radiation from the sun sustains life on earth and determines climate. The energy flow within the sun results in a surface temperature of around 5800 K, so the spectrum of the radiation from the sun is similar to that of a 5800 K blackbody with fine structure due to absorption in the cool peripheral solar gas.

You can estimate the power in the collimated beams* at any wavelength or in any wavelength range from our Series Q, Apex, or Research Lamp Housings with any of our CW and pulsed arc, quartz tungsten halogen or deuterium lamps.

Gratings are available in various groove densities (i.e. lines/mm). Higher groove densities give higher reciprocal dispersion and therefore higher resolution. The grating dispersion is similar for gratings with the same groove density. The exact dispersion is dependent upon other physical characteristics of the grating in addition to the groove density.

Oriel® Solar Simulators provide the closest spectral match to solar spectra available from any artificial source. The match is not exact, but better than needed for many applications. For the closest match possible, choose a Oriel Sol3A Class AAA Solar Simulator, these maintain an extremely tight uniformity, output stability and spectral match, as required by the photovoltaic cell manufacturers for testing PV cells.

Oriel products and solutions represent leading instruments, such as light sources covering a broad range from UV to IR, pulsed or continuous, and low to high power.

A solar simulator is a light source that approximates the illumination of natural sunlight. The ability of a solar simulator to approximate natural sunlight is based on three criteria: (1) spectral match, (2) spatial non-uniformity of irradiance and (3) temporal instability.

The radiometric data shown at the end of this section was measured in our Standards Laboratory. The wavelength calibrations are based on our spectral calibration lamps. Irradiance data from 250 to 2500 nm is based on an NIST traceable calibrated quartz tungsten halogen lamp.

Everything radiates and absorbs electro-magnetic radiation. Many important radiation laws are based on the performance of a perfect steady state emitter called a blackbody or full radiator. These have smoothly varying spectra that follow a set of laws relating the spectral distribution and total output to the temperature of the blackbody.

There are many systems of units for optical radiation. In this tutorial, we try to adhere to the internationally agreed CIE system. The CIE system fits well with the SI system of units. We work mostly with the units familiar to those working in the UV to near IR.

Spectral irradiance data is shown below for our Arc Lamps. You can click on the curve for a larger image, or on a model number for complete information on a specific arc lamp. Spectral irradiance curves for other types of lamps can be found on the right.

In a typical photo-research system, a detector measures the radiant intensity used to evoke photo-response in a sample or the radiant intensity produced by the sample in response to light or other simulation. The measurement is very frequently done after the beam has been separated into its component wavelengths.

The most accurate and economical method of wavelength calibration is the spectral calibration lamp. We offer lamps to cover wavelengths from below 185 nm to over 2.5 µm. Be sure to check out our popular battery powered Hg(Ar) calibration lamp, for the utmost in ease of use and portability.

This glossary briefly defines the terms and units most frequently used in technical discussions around solar simulation.

The spectral irradiance at any wavelength, Eλ, is in units of watts per square meter per nm (W m-2 nm-1). The value is a measure of the flux per nm at the specified wavelength incident normally onto an element of the surface divided by the area of the surface element in square meters.

Newport's PZA Ultra-High Resolution Actuator provides 12.5 mm travel with 50 N load capacity.